1. Field of the Invention
The invention relates to the field of electronic test equipment and electronic systems and, in particular, to a circuit design that provides an amplitude and temperature-insensitive signal-to-noise ratio for determining the performance of equipment such as radio receivers and the like.
2. Description of Related Art
Microwave thermal noise has long been employed for built-in test (BIT) of receivers and radiometers. Such systems are discussed in Microwave Journal article “Using Noise For RF Receivers Built In Test Applications” by Patrick Robbins, dated February, 2004. A common application using noise is to test the RF spectral gain/loss response of the front-end transmission line and microwave control components from the antenna through the RF receiver. The receiver then detects the noise signal, which, in theory, is flat over the frequency band. If the detector is swept over frequency, the system will have the spectral data of its front end.
If the noise source is used in conjunction with a received RF signal (either an over-the-air signal or an injected signal, wherein injected implies the signal is directly applied, for example, via a coaxial cable (or similar connection) or otherwise provided by the receiver itself) to create a known signal-to-noise ratio then it becomes important to closely control not only the level of the noise but also the level of the received signal. This becomes difficult as received signal levels fluctuate and the operating temperature of the system changes. A known signal-to-noise ratio produces a known performance level in the receiver.
Thus, it is a primary object of the invention to provide a circuit for generating a test signal to determine if an electronic communication system is working properly.
It is another primary object of the invention to provide a circuit for generating a test signal to determine if an electronic device is working properly by generating a controlled signal-to-noise ratio test signal.
It is a further object of the invention to provide a circuit for generating a test signal to determine if an electronic device is working properly by generating a controlled signal-to-noise ratio test signal that is independent of both the received signal amplitude and operating temperature.
It is a further object of the invention to provide a circuit for generating a test signal to determine if an electronic device is working properly by generating a controlled signal-to-noise ratio test signal that is independent of both the received signal amplitude and operating temperature wherein both the signal and noise are derived from the signal.